1. Field of the Invention
The present invention relates to a projection system, and more particularly, to a downsized projection system having improved condensing efficiency and uniformity of illumination.
2. Description of the Related Art
A projection system is largely classified into a three-panel projection system and a single-panel projection system depending on the number of display devices the projection system contains. The display devices perform on-off control on light emitted from a light source, which is a high-power lamp in units of pixels, to form a color image. In the single-panel projection system, the structure of an optical system can be reduced in comparison to the three-panel projection system, but white light is separated into red (R), green (G), and blue (B) colors using a sequential method. Thus, the photoefficiency of the single-panel projection system is reduced to 1/3 the photoefficiency of the three-panel projection system. Thus, efforts for increasing photoefficiency of the single-panel projection system have been made.
In a conventional single-panel projection system, a beam irradiated from a white light source is separated into R, G, and B color beams such as R, G, and B colors, using a color filter, and each color beam is sequentially transferred to a display device. The display device is operated in the order of the colors so as to form an image.
Display devices include liquid crystal displays (LCDs) and deformable mirror devices (DMDs).
The DMD has advantages such as having excellent heat resistance, high resolution and being of low cost. However, in order to use the DMD, a beam should be nearly orthogonally incident on the DMD. Due to this limitation, the number of optical devices in the system increases, and luminance is lowered accordingly.
In order to solve these problems, efforts for reducing the number of optical devices in the system have been made.
A conventional image display apparatus is disclosed in U.S. Pat. No. 6,129,437, and FIG. 1 is a structural diagram of the image display apparatus disclosed therein.
Referring to FIG. 1, the conventional image display apparatus comprises a white light source 50 having an arc 51 and an elliptical mirror 52; a color filter 53 which separates light emitted from the white light source 50 according to each color; a condensing lens 1 through which the light that has passed through the color filter 53 passes; a reflection mirror 2 which reflects the light that has passed through the condensing lens 1; a display device 56 which modulates the light reflected by the reflection mirror 2 in response to an input image signal to form a color image; and a projection lens unit 57 which includes first through fourth lenses 571, 572, 573, and 574 which enlarge and project the color image onto a screen 58. Here, reference numeral 60 denotes a glass rod or a fly-eye integrator.
The reflection mirror 2 is a single mirror having a concave shape arranged on a light path other than the light path defined by optical devices 56 through 58. In addition, the reflection mirror 2 is arranged to be eccentric with respect to the optical axis defined by the condensing lens 1 and the white light source 50.
In the above structure, the reflection mirror 2 is used to direct the light emitted from the light source 50 onto the display device 56. However, since the concave mirror has to condense a highly divergent beam, photoefficiency and uniformity of illumination are lowered.